Abstract
A ballistic pendulum tester for the absolute measurement of the energy (or work) of rupture of cords and yarns on impact is described, and the applied theory of the pendulum is briefly re viewed. Essentially, the test consists of placing a looped specimen, clamped at its ends, in a horizontal plane, so that it is struck in the bend of the loop by the pendulum at the bottom of its swing with sufficient energy to break the specimen. The difference in angular displacement of the pendulum with and without a specimen in place provides the measure of the energy lost in breaking the specimen.
For expressing the results of the test as applied to tirecord, with reference to various condi tions, four physical quantities have been defined. The significance of these quantities is dis cussed, and the results of exploratory tests on a number of rayon constructions are given, showing the application of the various measures.
By means of high-speed photography, used in connection with the pendulum apparatus, the impact rupture process in tirecord has been analyzed, and the energy separated into its force and elongation components. It is revealed that an experimental cord having higher-than-normal strength by the conventional test not only has a lower energy of rupture than a viscose con trol, but also appears to have lower impact strength. The analysis shows that the "breaking point," even in an impact test, is not an instantaneous phenomenon.
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